Disc screens as contemplated by the present invention are frequently used as one stage of a multi-stage materials separating system. Such a multi-stage system is illustrated in co-pending application, Ser. No. 841,168. FIG. 9 is a plan view of the disc screen which is also indicated by reference 56 in FIG. 1. Whereas the illustrated system is designed to separate out an intermixture of such debris as wood, rock and dirt accumulated in a lumber mill yard, the disc screen has further application for separation of refuse and all manner of materials where separation by size is an objective.
In general, the discs of a disc screen are mounted on shafts at spaced positions along the length of the shaft thereby forming disc rows. The shafts or disc rows are mounted in parallel with the discs of one disc row interspersed between the discs of adjacent (before and after) disc rows. Rectangular openings are formed by the spacing between the adjacent overlapping discs of adjacent disc rows in one dimension and by the spacing between adjacent shafts in the other dimension. Materials passing through the disc screen have to fit down through these openings.
The discs are rotated on the shaft in a direction from an inlet end to an outlet end. An admixture deposited on the inlet end of the disc screen will be rolled by the discs toward the outlet end with materials of the acceptable size passing through the screen and the rejected materials being rolled toward and off the outlet end of the screen.
Problems encountered by such disc screens, which are the object of the present invention, are twofold. Materials in such admixtures come in all manner of sizes, shapes and consistencies, i.e. they can be rock hard or paper soft. As the materials are rolled off one row of discs and onto another, there is a tendency for certain of the materials, i.e. those that are just oversized for the screen opening, to become lodged between the rows. The edges of certain of the discs are sometimes scalloped or lobed to assist in gripping and moving the materials along the rows. At any rate, the problem is not particularly significant except at the ends of the disc rows. If material becomes lodged between a last disc in the row and the sidewall of the screen housing, it can become jammed. Unjamming may require shutting the operation down and manually removing the jammed materials.
As concerns the second problem; the shaft-to-shaft dimension as described above as one of the dimensions for the screen openings, is actually made up of sleeve sections that surround an inner driven shaft. The sleeve sections also separate and space the discs along the shaft length. Previously, these sleeve sections were supported on the shafts by rails running along the length of the shaft welded directly to the discs. The problem encountered with this structure is that any deformity of the discs (as when occasionally a disc is severely struck by a rock-hard object) would skew the sleeve section and create an interference between the close fitting sleeve sections and the aligned discs of the adjacent rows of discs.